1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device which has at least a capacitance element comprising a high dielectric thin film sandwiched with electrode materials and can prevent cracking in the high dielectric thin film.
2. Description of the Related Art
A junction-type capacitor, an MOS-type capacitor, an MIS-type capacitor, and the like are capacitance elements which may be integrated into a semiconductor integrated circuit device. The junction-type capacitor uses a PN-junction capacitance. The MOS-type capacitor uses a silicon oxide film sandwiched between a diffusion region (or lower electrode) and an upper metal electrode. The MIS-type capacitor uses a silicon nitride film having a higher dielectric constant instead of the silicon oxide film. Without using the diffusion region, both the upper and lower electrodes can be made of an electrode wiring material for sandwiching the dielectric thin film there between. This structure can cancel a voltage dependency of a capacitance value because it has no variation in resistance.
FIGS. 7A and 7B show a conventional structure of the capacitance element. FIG. 7A is a plan view showing a structure of the capacitance element described above. FIG. 7B is a cross-sectional view taken along line F--F in FIG. 7A. Referring to FIGS. 7A and 7B, a lower electrode 2 of a polycrystalline silicon film is formed on a LOCOS (local oxidation) oxide film 1 formed on a semiconductor substrate. A silicon nitride film 5 is deposited so as to cover the opening 4 in the interlayer insulating film 3. An upper electrode 6 is formed on the silicon nitride film 5 using a part of an aluminum wiring electrode 3. An aluminum take-out electrode 8 is electrically in contact with the lower electrode 2 via a contact hole 7 in the interlayer insulating film 3. The capacitance element having the above mentioned structure is disclosed, for example, in Japanese laid-open Patent Publication 2-226755.
For the latest semiconductor integrated circuit devices, a smoothing technique is indispensably adopted for smoothing steps formed on a surface to establish high density electrode wiring. A reflowing process of an interlayer insulating film is one of the most typical smoothing techniques. Boron-phosphosilicate glass (BPSG) has been widely used as a reflowing material. In this technique, a BPSG film is heated, and then thermally softened to absorb the underlying steps so that the shape of an opening is smoothed. In order to integrate a capacitance element using the reflowing technique, a silicon nitride film 5 is deposited onto the opening 4 formed in the BPSG film.
However, it has been apparent that a boron-phosphosilicate glass (BPSG) film used as the interlayer insulating film 3 causes a crack 9 in the silicon nitride film 5 positioned at the bottom of the opening 4, and thus frequently causes electrical short circuits between the upper electrode 6 and the lower electrode 2.
The inventors of the present invention have made a study on the causes of such short circuits, and it has been discovered that the cracking occurs when the silicon nitride film 5 is deposited, but does not occurs during the thermal process after the deposition of the silicon nitride film 5.
Normally, the deposition temperature of the silicon nitride film 5 in a LPCVD process ranges from 700.degree. C. to 800.degree. C. The reflow temperature of a BPSG film is about 900.degree. C. Hence, it is considered that the BPSG film is unaltered in shape at the deposition temperature of the silicon nitride film 5.
However, it is considered that since a thermal expansion coefficient of the BPSG film is substantially different from the silicon nitride 5, the BPSG film is excessively deformed by an effect of a stress in the direction of the arrow 10 (shown in FIG. 7B) which is applied from the silicon nitride film 5 to the BPSG film 3, in addition to the reduction force of the BPSG film 3. It is inferred that since the BPSG film 3 is excessively deformed, a stress is applied to the silicon nitride film 5, which causes the crack 9.